JPS63303021A - Cu-nb powder metallurgy preform - Google Patents

Abstract

PURPOSE:To improve the plastic workability of the titled preform by regulating the oxygen content in the Cu-Nb powder metallurgy preform as the material of an Nb3Sn superconductive material to the specific ratio or below for the Nb content. CONSTITUTION:Powdery NbH and Cu are mixed in such a manner that the Nb amt. is regulated to 10-50wt.% and are sintered in a vacuum by hot isostatic pressing to produce the Cu-Sb powder metallurgy preform. In this case, the Nb content in the Cu-Sb powder metallurgy preform is regulated to 10-50wt.% and the oxygen content is regulated to the amt. which is expressed by the following inequality (O) <=15 (Nb), where the unit of (O) is specified to ppm and the unit of (Nb) is specified to %. Since said powder metallurgy preform has excellent plastic workability and is easily formed into a long size wire rod, it can efficiently be utilized as the material for a superconductive material such as an Nb3-Sn super conductive wire rod, etc.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to Cu, which is a raw material for Nb and Sn-based superconducting materials.
The present invention relates to a -Nb powder metallurgy molded body, and specifically relates to a Cu-Nb powder metallurgy molded body that has good plastic workability and provides excellent superconducting properties.

[Prior art] N1gSn, which is one of the A-15 type compound superconducting wires
BACKGROUND ART Superconducting wires have attracted attention as wires for superconducting magnets that generate high magnetic fields because they have a large critical current density under high magnetic fields.

Nb3Sn-based superconducting wires have conventionally been manufactured by a bronze method, but this method has drawbacks such as complicated steps and significant deterioration of superconducting properties due to strain. Therefore, as a wire material that overcomes these drawbacks, a so-called In-5 wire material in which ultrafine superconducting fibers are dispersed discontinuously in a Cu matrix is proposed.
ITU superconducting wire has been developed and has succeeded in obtaining superconducting properties superior to those of the bronze method.

To explain the basic manufacturing method of Nb and Sn superconducting wires using the In-5itu method, Cu-Nb raw materials prepared to have an Nb content of 10 to 50% are melted and cast in vacuum or inert gas. , producing a Cu-Nb ingot. This Cu-Nb ingot exhibits a metal structure in which Nb dendrite crystals are precipitated in a resin-like manner in the Cu matrix, since almost no Nb is solidly dissolved in the Cu matrix.

Next, when the Cu--Nb ingot is subjected to surface reduction processing to form a long wire rod, the Nb dendrite crystals are stretched, resulting in a structure in which fibrous dendrite crystals are discontinuously dispersed in the Cu matrix. Next, after applying Sn plating on the surface of the long wire rod, heat treatment at a temperature of 500 to 750°C results in S
n diffuses into Cu and reacts with Nb, forming a Nb, Sn-based superconducting compound.

However, in the In-5itu method, the shape and size of Nb dendrite crystals in the Cu-Nb ingot are sensitively influenced by the cooling rate during melting and casting, and the shape and size of the crystals in the longitudinal and radial directions of the ingot are If the distribution of the Nb dendrite structure in the Cu-Nb ingot is uneven, the Nb
The distribution of the 3Sn-based superconducting compound also becomes non-uniform, and as a result, the uniformity of the superconducting properties [critical current density (Jc) properties] is lost.

On the other hand, as a method for solving the above-mentioned non-uniformity of the Cu--Nb ingot metal structure, there is a method of forming Cu powder and Nb powder by a powder metallurgy technique. In this method, first, Cu powder and Nb powder are mixed, compression molded, and then fired to produce a Cu-Nb powder metallurgical compact. The obtained molded body is a sintered body in which Nb is uniformly dispersed, and when this is subjected to area reduction processing to form a long wire rod, the surface is polished with Sn, and then heat treated, Sn is mixed into Cu. Through diffusion, a Nb and Sn-based superconducting compound is generated. According to this method, a Cu--Nb powder metallurgical compact having a substantially uniform structure can be obtained by adjusting the particle size of the raw material powder and sufficiently mixing the powder.

However, Cu--Nb powder metallurgy compacts have poor plastic workability compared to cast materials, and cracks have often occurred when the compacts are made into long wire rods. In addition, because Nb is uniformly dispersed, the distribution of the superconducting compound is also uniform, and good superconducting properties should be obtained.However, in reality, there are variations in the properties, and the desired stable superconducting properties cannot be obtained. The problem was that there was no.

[Problems to be Solved by the Invention] The present invention has been made with attention to these circumstances, and it is a Cu-Nb powder metallurgy forming method that provides good plastic workability and excellent superconducting properties. The purpose is to provide the body. In particular, as is clear from the above explanation, it is not possible to obtain a homogeneous Nb distribution structure with ingot material, so even if the plastic workability is good, it is theoretically difficult to obtain uniform superconducting properties. Specifically, the present invention was completed as a result of adopting a powder metallurgy compact, taking advantage of its advantage of homogeneity of structure, and proceeding with the improvement of plastic workability.

[Means for solving the problems] The present invention, which has achieved the above object, has N in the Cu base material.
A Cu-Nb powder metallurgy molded body in which b particles are dispersed,
Nb content is 10 to 50% (meaning of weight %, the same applies hereinafter)
In addition, the gist is that the 0 content satisfies the following formula.

[o]≦xs[Nb] ”-(1) However, [O] is an anonymous number when the 0 content is expressed in ppm, and [Nb] is an anonymous number when the Nb content is expressed in %. ] As a result of various studies on the factors that inhibit plastic workability in Cu-Nb powder metallurgy compacts, it was determined that the cause lies in the presence of Nb oxide. That is, Nb is an active metal and is easily contaminated by oxygen. Therefore, commercially available Nb
Generally, the surface of the raw material powder is highly oxidized, and the oxygen content reaches 1000 to SOOO ppm. In this way, when the Nb raw material powder is directly mixed with the Cu powder, molded and sintered to form a compact, Nb is dispersed in the Cu base.
Oxygen is dissolved in solid solution in the b particles, and the hardness of the Nb particles increases significantly. As a result, when the molded body is subjected to surface reduction processing, since the Nb particles are difficult to plastically deform, stress concentration occurs starting from the Nb particles, causing cracks.

In particular, the hardening of Nb particles becomes remarkable when hot working is performed at 500°C or higher.

In addition, in a Cu-Nb powder metallurgy compact in which Nb particles hardened by solid solution of oxygen are dispersed, even if processing is achieved in the final shape, S
The reactivity of n and Nb particles decreases, resulting in a decrease in the amount and characteristics of Nb and Sn produced, making it impossible to obtain desired superconducting characteristics.

The inventors of the present invention paid attention to these circumstances and, as a result of further studies, completed the present invention shown in the above configuration.

The effects of the present invention will be explained below along with the background of the research.

According to the above considerations, if oxygen solidly dissolves in Nb particles and hardens, plastic workability deteriorates and cracks occur, so first, Cu-Nb powder metallurgy compacts with various compositions are created
After measuring the Vickers hardness of each particle, the molded body was wire drawn according to a conventional method, and the relationship between Nb particle hardness and wire drawability was investigated.

Note that the Nb content and 0 content were measured simultaneously with the hardness measurement of the Cu-Nb powder metallurgy compact before wire drawing. As a result, it was found that there is a relationship between Nb particle hardness and wire drawability in that when the hardness exceeds a certain value, wire drawability decreases rapidly, confirming that the above consideration is correct.

Next, the wire rod obtained by wire drawing is treated with S according to a conventional method.
When the critical current Ic of superconducting wire obtained by heat treatment after n plating was measured, it was found that there was a correlation between the hardness and the critical current 1c, and when the hardness exceeded a certain value, Ic
was found to be significantly reduced. From these results, if a Cu-Nb powder metallurgy compact is prepared so that the hardness is below a certain value, excellent plastic workability and critical current value Ic can be achieved.
It was confirmed that a Cu-Nb powder metallurgy compact giving the following properties could be obtained. Therefore, as a result of considering a specific structure to keep the hardness below a certain value, it was found that there is a correlation between the hardness of the Cu-Nb powder metallurgy compact and the O content and Nb content,
It is clear that if the 0 content satisfies the above formula (1), the hardness can be reduced to a desired value or less, and a Cu-Nb powder metallurgy compact can be obtained that provides excellent plastic workability and superconducting properties. .

That is, in the present invention, in order to obtain excellent plastic workability and superconducting properties, [O] needs to be 15 times or less than [Nb], and if [O] exceeds 15 times [Nb], Nb If the hardness of the particles becomes too high, plastic workability deteriorates, and a satisfactory value for superconducting properties cannot be obtained, and the Nb content must be adjusted to ensure the necessary amount of superconducting material (Nb3Sn) to obtain good superconducting properties. In order to obtain this, it is necessary to set it to 10% or more. However, when the Nb content exceeds 50%, the superconducting properties decrease by 40%N
Although the b content is almost the same, processing becomes extremely difficult.

[Example] NbH powder of 105 to 149 μm and spherical C of various particle sizes
U powder was blended to have a composition of Cu-10 to 45% by weight Nb, and mixed for 15 minutes using a V-type mixer. The obtained mixed powder was placed in a HIP capsule [50 x 60
' x 2.5t (mm)] with tap density.

I filled it.

When this was heated to 850° C. while being evacuated by an oil diffusion pump, H2 was generated during heating, and after 3 hours, the vacuum level returned to 10-'torr before heating. This capsule was vacuum-sealed and HIPfi-embedded (600℃ x 1500gf/
cm' x 2 hr) to obtain a Cu-Nb superconducting member of 36 x 40' (av+).

The results of measuring the Vickers hardness (load!!50g) of the Nb particles in the obtained Cu-Nb member are shown in Table 1.
The results in the table are summarized in terms of Nb content [Nb] (wt%) and oxygen concentration [O] (ppm) as shown in Figure 1. Furthermore, the Vickers hardness Hv (kg/nu11') of the Nb particles is added to each point in the figure. Note that the area marked with diagonal lines in FIG. 1 is the scope of the present invention.

[O] in the Cu-Nb member is Cu with various [O]
Stinging was done by using powder.

That is, the coarser the Cu powder, the lower the [O], and some of the Cu powder was reduced to an even lower value by H2 reduction.

Table 1 Among the samples in Table 1, sample No. 4.5, 6, 7°8.9
．． 10 was inserted into a Cu tube with an outer diameter of 42 mm and an inner diameter of 361 nIIl, vacuum-sealed to form an extruded billet, and after reducing the area to 8 (I! 1 IB) by hot isostatic extrusion at 600°C, it was rolled to 1.0 + ( mm). Subsequently, the wire was drawn to a diameter of 0.25 mm (I11!I) using a wire drawing die, and the wire drawability was evaluated (the results are also listed in Table 1). For wire drawability, wires that could be drawn up to 0.25 mm without annealing were marked with ◎, and for others, the number of times of annealing was written. The length of each long line obtained is approximately 1.1 km.
Met. This long wire is plated with approximately 6 to 9 μm of Sn, and after a preliminary heat treatment of 450°C x 5 hr in vacuum, a diffusion heat treatment of 700°C x 60 hr is performed.
An n-superconducting wire was obtained.

This sample (No. 4 to 10) was heated at a critical current of 1 in a magnetic field of 8 T.
The results of the measurement of c are also listed in Table 1. This is N
FIG. 2 shows the relationship between the Vickers hardness Hv of the b particles. Samples within the scope of the present invention are 2 to 2 of the samples outside the range.
It was found that 4 times the value was obtained. In order to investigate the cause of this difference in superconducting properties, we measured the Hv measurement number of Nb particles after extrusion.

9. When conducted on 10 samples, each yielded 21
0 kg/ll1m2. 161 kg/am2, indicating that there was significant solid solution of [O] in sample No. 8 during hot working.

[Effects of the Invention] The present invention is configured as described above, and according to the present invention, it is possible to reliably obtain a Cu-Nb powder metallurgy compact that provides a superconducting wire having excellent plastic workability and excellent superconducting properties. be able to.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between oxygen concentration and Nb content and Nb particle hardness in a Cu-Nb powder metallurgy compact;
The figure is a graph showing the relationship between Nb particle hardness and critical current 1c.

Claims (1)

[Scope of Claims] A Cu-Nb powder metallurgy molded body in which Nb particles are dispersed in a Cu base material, the Nb content being 10 to 50% (meaning % by weight, hereinafter the same), and containing O. A Cu-Nb powder metallurgical compact for manufacturing a superconducting member, characterized in that the amount thereof satisfies the following formula. [O]≦15[Nb]...(1) However, [O] is an anonymous number when the O content is expressed in ppm units [Nb] is an anonymous number when the Nb content is expressed in % units.